Method for feeding backchannel state information, user equipment, and base station

ABSTRACT

Embodiments of the present invention provide a method for feeding back channel state information, a user equipment, and a base station, to improve feedback precision of channel state information. The method includes: receiving a reference signal sent by a base station; selecting a precoding matrix W from a codebook according to the reference signal, where a column vector of the precoding matrix W may be expressed as α[v e jφ v] T , v=[1 e jθ ]; and sending a precoding matrix indicator PMI to the base station, where the PMI is corresponding to the selected precoding matrix W. The present invention may further improve quantization precision and achieve balance between overheads and the quantization precision. The base station performs precoding on a sent signal according to a fed back precoding matrix indicator, which can improve precoding precision, thereby improving a data transmission rate and system throughput.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2012/087699, filed on Dec. 27, 2012, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of mobile communications, andin particular, to a method for feeding back channel state information, auser equipment, and a base station.

BACKGROUND

A multiple-input multiple-output (MIMO) wireless communication systemmay obtain diversity and array gains by using beam forming (BF) andreceive signal combination, or by using precoding and receive signalcombination. Typically, a wireless communication system using BF orprecoding may be generally expressed as y=HVs+n, where y is a receivedsignal vector, H is a channel matrix, V is a precoding matrix, s is atransmitted symbol vector, and n is measurement noise. Generally,optimal precoding requires that channel state information (CSI) is fullyknown to a transmitter, and a commonly used method is that a userequipment (UE) performs quantization on instantaneous CSI and feeds backthe quantized instantaneous CSI to a node B (NodeB). CSI fed back by anexisting Long Term Evolution Release 8 (LTE R8) system includes a rankindicator (RI), a precoding matrix indicator (PMI), a channel qualityindicator (CQI), and the like, where the RI and the PMI respectivelyindicate the number of used layers and a precoding matrix. Generally, aset of used precoding matrices is called a codebook, and each precodingmatrix in the codebook is called a code word. A codebook of LTE R8 ismainly designed for single user multiple-input multiple-output(SU-MIMO), where a precoding matrix or a code word is restrained by 8phase shift keying (8PSK), and precision of spatial quantization islimited. For a transmission manner in which precision of spatialquantization is sensitive, such as multiple user multiple-inputmultiple-output (MU-MIMO), performance of the transmission manner isseverely limited by the codebook of LTE R8. To meet a higher systemrequirement, a 3rd Generation Partnership Project (3GPP) LTE systemneeds to further enhance performance of MU-MIMO. In addition, acoordinated multiple-points (CoMP) transmission technology is introduced(currently, CoMP is based on a single-cell feedback). The foregoing twotechnologies both have a higher requirement on feedback performance.

In the prior art, a single codebook is used to feed back RIs and PMIs.By using four antennas as an example, a correspondence between an RI, aPMI, and each code word in the codebook is shown in the following Table1:

TABLE 1 RI PMI u_(n) 1 2 3 4 0 u₀ = [1 −1 −1 −1]^(T) W₀ ^({1}) W₀^({14})/{square root over (2)} W₀ ^({124})/{square root over (3)} W₀^({1234})/2 1 u₁ = [1 −j 1 j]^(T) W₁ ^({1}) W₁ ^({12})/{square root over(2)} W₁ ^({123})/{square root over (3)} W₁ ^({1234})/2 2 u₂ = [1 1 −11]^(T) W₂ ^({1}) W₂ ^({12})/{square root over (2)} W₂ ^({123})/{squareroot over (3)} W₂ ^({3214})/2 3 u₃ = [1 j 1 −j]^(T) W₃ ^({1}) W₃^({12})/{square root over (2)} W₃ ^({123})/{square root over (3)} W₃^({3214})/2 4 u₄ = [1 (−1 − j)/{square root over (2)} −j (1 − j)/{squareroot over (2)}]^(T) W₄ ^({1}) W₄ ^({14})/{square root over (2)} W₄^({124})/{square root over (3)} W₄ ^({1234})/2 5 u₅ = [1 1 − j)/{squareroot over (2)} j (−1 − j)/{square root over (2)}]^(T) W₅ ^({1}) W₅^({14})/{square root over (2)} W₅ ^({124})/{square root over (3)} W₅^({1234})/2 6 u₆ = [1 (1 + j)/{square root over (2)} −j (−1 + j)/{squareroot over (2)}]^(T) W₆ ^({1}) W₆ ^({13})/{square root over (2)} W₆^({134})/{square root over (3)} W₆ ^({1324})/2 7 u₇ = [1 (−1 +j)/{square root over (2)} j (1 + j)/{square root over (2)}]^(T) W₇^({1}) W₇ ^({13})/{square root over (2)} W₇ ^({134})/{square root over(3)} W₇ ^({1324})/2 8 u₈ = [1 −1 1 1]^(T) W₈ ^({1}) W₈ ^({12})/{squareroot over (2)} W₈ ^({124})/{square root over (3)} W₈ ^({1234})/2 9 u₉ =[1 −j −1 −j]^(T) W₉ ^({1}) W₉ ^({14})/{square root over (2)} W₉^({134})/{square root over (3)} W₉ ^({1234})/2 10 u₁₀ = [1 1 1 −1]^(T)W₁₀ ^({1}) W₁₀ ^({13})/{square root over (2)} W₁₀ ^({123})/{square rootover (3)} W₁₀ ^({1324})/2 11 u₁₁ = [1 j −1 j]^(T) W₁₁ ^({1}) W₁₁^({13})/{square root over (2)} W₁₁ ^({134})/{square root over (3)} W₁₁^({1324})/2 12 u₁₂ = [1 −1 −1 1]^(T) W₁₂ ^({1}) W₁₂ ^({12})/{square rootover (2)} W₁₂ ^({123})/{square root over (3)} W₁₂ ^({1234})/2 13 u₁₃ =[1 −1 1 −1]^(T) W₁₃ ^({1}) W₁₃ ^({13})/{square root over (2)} W₁₃^({123})/{square root over (3)} W₁₃ ^({1324})/2 14 u₁₄ = [1 1 −1 −1]^(T)W₁₄ ^({1}) W₁₄ ^({13})/{square root over (2)} W₁₄ ^({123})/{square rootover (3)} W₁₄ ^({3214})/2 15 u₁₅ = [1 1 1 1]^(T) W₁₅ ^({1}) W₁₅^({12})/{square root over (2)} W₁₅ ^({123})/{square root over (3)} W₁₅^({1234})/2

W_(s) ^({s}) indicates a matrix that includes a column set {s} of amatrix W_(n)=I−2u_(n)u_(n) ^(H)/u_(n) ^(H) _(n), where I is a 4×4identity matrix, and u_(n) is provided by the foregoing table. In anexisting LTE R8 system, there are two PMI feedback manners: one manneris that one PMI is fed back for entire system bandwidth; and the othermanner is that, the system is divided into multiple bandwidth parts (BP)and each BP includes multiple sub-bands (sub-band), and PMIs are fedback for different sub-bands. The former manner is generally calledbroadband PMI, and the latter manner is generally called sub-band PMI.

It can be learned from thorough investigation on the foregoing Table 1that, in a precoding matrix obtained based on W_(n)=I−2u_(n)u_(n)^(H)/u_(n) ^(H) _(n) in the prior art, a phase of each element issubject to an 8PSK restraint; that is, a phase difference betweendifferent elements is a multiple of π/4, and it is difficult to describea smaller spatial granularity difference, such as a phase difference ofπ/16 or π/8 between antenna ports. Therefore, feedback precision of CSIis reduced, and it is difficult to meet a feedback precision requirementof a technology such as MU-MIMO or CoMP transmission.

SUMMARY

Embodiments of the present invention provide a method for feeding backchannel state information, a user equipment, and abase station, toimprove feedback precision of channel state information.

According to a first aspect, an embodiment of the present inventionprovides a method for feeding back channel state information, where themethod includes:

receiving a reference signal sent by a base station;

selecting a precoding matrix W from a codebook according to thereference signal, where a column vector of the precoding matrix W may beexpressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θand φ are phases, and [ ]^(T) indicates transposing of a matrix orvector; and

sending a precoding matrix indicator PMI to the base station, where thePMI is corresponding to the selected precoding matrix W.

With reference to the first aspect, in a first possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\begin{Bmatrix}{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\{- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},} \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\1 & 1 & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & ^{j\theta} \\1 & 1 & {- 1} \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}}\end{bmatrix}}}\end{Bmatrix}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates the greatest integer not greater than i₂/4.

With reference to the first aspect, in a second possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\1 & 1 & {- 1} & {- 1} \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\j & j & {- j} & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}} & {- {j}^{j\theta}} & {j}^{j\theta}\end{bmatrix}}} \right\}$ or $\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\1 & {- 1} & 1 & {- 1} \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\j & {- j} & j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}} & {- {j}^{j\theta}} & {j}^{j\theta}\end{bmatrix}}} \right\}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/2┘ indicates the greatest integer not greater than i₂2.

With reference to the first or second implementation manner, in a thirdpossible implementation manner, where the sending a precoding matrixindicator PMI to the base station comprises: sending a first precodingmatrix indicator PMI₁ and a second precoding matrix indicator PMI₂ tothe base station, wherein the first precoding matrix indicator PMI₁ andthe second precoding matrix indicator PMI₂ are respectively used toindicate indexes i₁ and i₂ corresponding to the selected precodingmatrix W.

According to a second aspect, an embodiment of the present inventionfurther provides a method for feeding back channel state information,where the method includes:

sending a reference signal to a user equipment UE;

receiving a precoding matrix indicator PMI sent by the UE, where the PMIis corresponding to a precoding matrix W that is selected by the UE froma codebook based on the reference signal, and a column vector of theprecoding matrix W may be expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)],where α is a constant, θ and φ are phases, and [ ]^(T) indicatestransposing of a matrix or vector.

With reference to the second aspect, in a first possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\begin{Bmatrix}{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\{- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},} \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\1 & 1 & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & ^{j\theta} \\1 & 1 & {- 1} \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}}\end{bmatrix}}}\end{Bmatrix}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates the greatest integer not greater than i₂/4.

With reference to the second aspect, in a second possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\1 & 1 & {- 1} & {- 1} \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\j & j & {- j} & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}} & {- {j}^{j\theta}} & {j}^{j\theta}\end{bmatrix}}} \right\}$ or $\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\1 & {- 1} & 1 & {- 1} \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\j & {- j} & j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}} & {- {j}^{j\theta}} & {j}^{j\theta}\end{bmatrix}}} \right\}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂2┘ indicates the greatest integer not greater than i₂/4.

With reference to the first or second implementation manner, in a thirdpossible implementation manner, where the receiving a precoding matrixindicator PMI sent by the UE comprises: receiving a first precodingmatrix indicator PMI₁ and a second precoding matrix indicator PMI₂ thatare sent by the UE, wherein the first precoding matrix indicator PMI₁and the second precoding matrix indicator PMI₂ are respectively used toindicate indexes i₁ and i₂ corresponding to the selected precodingmatrix.

A third aspect of the present invention provides a user equipment, wherethe user equipment includes:

a receiving module, configured to receive a reference signal sent by abase station;

a selecting module, configured to select a precoding matrix W from acodebook based on the reference signal received by the receiving module,where a column vector of the precoding matrix W may be expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector; and

a sending module, configured to send a precoding matrix indicator PMI tothe base station, where the PMI is corresponding to the precoding matrixW selected by the selecting module.

With reference to the third aspect, in a first possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\begin{Bmatrix}{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}} \\1 & {- 1} & {- 1} \\{- ^{j\theta}} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},} \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\theta} & {- ^{j\theta}} & {- ^{j\theta}} \\1 & 1 & {- 1} \\^{j\theta} & {- ^{j\theta}} & ^{j\theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\theta}} & ^{j\theta} & ^{j\theta} \\1 & 1 & {- 1} \\{- ^{j\theta}} & ^{j\theta} & {- ^{j\theta}}\end{bmatrix}}}\end{Bmatrix}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates the greatest integer not greater than i₂/4.

With reference to the third aspect, in a second possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\theta} & {- ^{j\; \theta}} \\1 & 1 & {- 1} & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\j & j & {- j} & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}$$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\theta}} & {- ^{j\; \theta}} \\1 & {- 1} & 1 & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\; \theta}} & {- ^{j\; \theta}} \\j & {- j} & j & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/2┘ indicates the greatest integer not greater than i₂/2.

With reference to the first or second implementation manner, in a thirdpossible implementation manner, where the sending module is specificallyconfigured to: send a first precoding matrix indicator PMI₁ and a secondprecoding matrix indicator PMI₂ to the base station, wherein the firstprecoding matrix indicator PMI₁ and the second precoding matrixindicator PMI₂ are respectively used to indicate indexes i₁ and i₂corresponding to the selected precoding matrix.

Correspondingly, a fourth aspect of the present invention furtherprovides a base station, where the base station includes:

a second sending module, configured to send a reference signal to a userequipment UE;

a second receiving module, configured to receive a precoding matrixindicator PMI sent by the UE, where the PMI is corresponding to aprecoding matrix W that is selected by the UE from a codebook based onthe reference signal, and a column vector of the precoding matrix W maybe expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θand φ are phases, and indicates transposing of a matrix or vector.

With reference to the fourth aspect, in a first possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\begin{Bmatrix}{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\; \theta} & ^{j\theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\^{{j\; \theta}\;} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\{- ^{j\; \theta}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},} \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\; \theta} & {- ^{j\theta}} & {- ^{j\; \theta}} \\1 & 1 & {- 1} \\^{{j\; \theta}\;} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\; \theta}} & ^{j\; \theta} & ^{j\; \theta} \\1 & 1 & {- 1} \\{- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}}\end{bmatrix}}}\end{Bmatrix}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates the greatest integer not greater than i₂/4.

With reference to the fourth aspect, in a second possible implementationmanner, where the precoding matrix W is at least one matrix in thefollowing matrix set:

$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\theta} & {- ^{j\; \theta}} \\1 & 1 & {- 1} & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\j & j & {- j} & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}$$\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\theta}} & {- ^{j\; \theta}} \\1 & {- 1} & 1 & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\; \theta}} & {- ^{j\; \theta}} \\j & {- j} & j & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\}$${{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/2┘ indicates the greatest integer not greater than i₂/2.

With reference to the first or second implementation manner, in a thirdpossible implementation manner, where the second receiving module isspecifically configured to: receive a first precoding matrix indicatorPMI₁ and a second precoding matrix indicator PMI₂ that are sent by auser equipment to the base station, wherein the first precoding matrixindicator PMI₁ and the second precoding matrix indicator PMI₂ arerespectively used to indicate indexes i₁ and i₂ corresponding to theselected precoding matrix.

Correspondingly, another embodiment of the present invention provides acomputer storage medium, where the computer storage medium may store aprogram, and when the program is executed, a step in the foregoingmethod embodiments is performed.

It can be learned from the foregoing embodiments of the presentinvention that, a user equipment may select a precoding matrix from acodebook based on a received reference signal, and send a precodingmatrix indicator corresponding to the selected precoding matrix W to thebase station, where the codebook includes at least one precoding matrixW, and a column vector of the precoding matrix W may be expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector. The foregoingcodebook structure may match actually deployed antenna configuration,for example, configuration of a four-port dual-polarized antenna or auniform linear array antenna; phases θ and φ are flexibly selected,which cannot only further improve quantization precision as required,but also achieve balance between overheads and the quantizationprecision. In addition, column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which can improve precodingprecision, thereby improving a data transmission rate and systemthroughput.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly introduces theaccompanying drawings required for describing the prior art or theembodiments. Apparently, the accompanying drawings in the followingdescription show merely some embodiments of the present invention, and aperson skilled in the art may still derive other drawings from theseaccompanying drawings.

FIG. 1 is a schematic flowchart of a method for feeding back channelstate information according to an embodiment of the present invention;

FIG. 2 is a schematic flowchart of a method for feeding back channelstate information according to another embodiment of the presentinvention;

FIG. 3 is a schematic structural diagram of a system for feeding backchannel state information according to an embodiment of the presentinvention;

FIG. 4 is a schematic structural diagram of a user equipment accordingto an embodiment of the present invention; and

FIG. 5 is a schematic structural diagram of a base station according toan embodiment of the present invention.

DETAILED DESCRIPTION

The following clearly describes the technical solutions in theembodiments of the present invention with reference to the accompanyingdrawings in the embodiments of the present invention. Apparently, thedescribed embodiments are merely some but not all of the embodiments ofthe present invention. All other embodiments obtained by a personskilled in the art based on the embodiments of the present inventionshall fall within the protection scope of the present invention.

Referring to FIG. 1, FIG. 1 is a schematic flowchart of a method forfeeding back channel state information according to an embodiment of thepresent invention, and an execution body of the method may be a userequipment (UE) of an LTE system, for example, may be a user equipment(UE), a mobile station (MS), or a relay (hereinafter referred to as aUE).

The following describes the method illustrated in FIG. 1, which mainlyincludes step S101, step S102, and step S103.

Step S101: Receive a reference signal sent by a base station.

In this embodiment of the present invention, the reference signal sentby the base station may include a channel state information referencesignal (CSI RS), a demodulation reference signal (DM RS), acell-specific reference signal (CRS), or the like. The user equipmentmay obtain the reference signal by receiving an eNB notification, forexample, by receiving radio resource control (RRC) signaling or downlinkcontrol information (DCI); or the user equipment obtains resourceconfiguration of the reference signal based on a cell identity ID andthen obtains the reference signal from a corresponding resource orsubframe. This embodiment of the present invention sets no limitation ona specific manner of receiving a reference signal.

It should be understood that the foregoing reference signal iscorresponding to an antenna port; the reference signal may becorresponding to a physical antenna or an antenna array element, ormaybe corresponding to a virtual antenna, where the virtual antenna is aweighted combination of a physical antenna and an antenna array element.

Step S102: Select a precoding matrix W from a codebook based on thereference signal, where a column vector of the precoding matrix W may beexpressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θand φ are phases, and [ ]^(T) indicates transposing of a matrix orvector.

Specifically, values of phases θ and φ may be flexibly selectedaccording to a requirement of quantization precision.

Further, column vectors of the precoding matrix W may be orthogonal toeach other, that is, W meets W^(H)W=α²I, where W^(H) indicates aconjugate transpose of the matrix W, and I is an identity matrix. Theforegoing structure divides antenna ports into two groups; a vector vmay match channel characteristics corresponding to each antenna group ofthe two groups, and a phase between the two antenna port groups may beexpressed by φ. The foregoing structure may match actually deployedantenna configuration, for example, configuration of a four-portdual-polarized antenna or a uniform linear array antenna. Phases θ and φare flexibly selected, which cannot only further improve quantizationprecision as required, but also achieve balance between overheads andthe quantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

It should be noted that, a codebook in this embodiment of the presentinvention may be a codebook subset. The codebook subset may bepredefined; the codebook subset may be reported by a user equipment to abase station (eNB), and then the base station (eNB) determines thecodebook subset based on reporting of the user equipment and notifiesthe user equipment of the determined codebook subset; or the codebooksubset may be a codebook subset determined and reported by a userequipment, for example, a recently reported codebook subset.

Specifically, in step 102, the selecting a precoding matrix from acodebook based on the reference signal may include: acquiring, by a UE,a channel estimation value based on the reference signal; and selecting,by the UE, a precoding matrix from a codebook based on the channelestimation value.

It should be noted that, this embodiment of the present invention setsno limitation on a specific manner of selecting a precoding matrix.Optionally, a precoding matrix is selected from the codebook accordingto a predefined criterion, such as a criterion of channel capacity orthroughput maximization, or a criterion of chordal distanceminimization. Selecting a precoding matrix based on a predefinedcriterion is an existing technology, and details are not describedherein again.

As an embodiment of the present invention, the precoding matrix W is atleast one matrix in the following matrix set:

$\begin{matrix}{\left\{ {{\frac{1}{2}\begin{bmatrix}1 \\^{j\; \theta} \\1 \\^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\; \theta} \\j \\{j\; ^{j\; \theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- 1} \\{- ^{j\; \theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{{- j}\;} \\{- {j}^{j\theta}}\end{bmatrix}}} \right\} {{{{where}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,}} & (1)\end{matrix}$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

It can be learned from investigation on the matrix set (1) to which theforegoing precoding matrix W belongs that, the foregoing precodingmatrix W may match actually deployed antenna configuration. In addition,a granularity of a value of θ is π/16, which may achieve more precisespatial quantization, and therefore feedback precision of CSI can beimproved.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the following matrix set:

$\begin{matrix}{\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\1 & {- 1} \\^{j\theta} & {- ^{j\theta}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\j & {- j} \\{j}^{j\theta} & {- {j}^{{j\theta}\;}}\end{bmatrix}}} \right\} {or}} & (2) \\{\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\1 & {- 1} \\^{j\theta} & {- ^{j{({\theta + \phi})}}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\j & {- j} \\{j}^{j\theta} & {- {j}^{j{({\theta + \phi})}}}\end{bmatrix}}} \right\} {{{{where}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},}} & \left( 2^{\prime} \right)\end{matrix}$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

It can be learned from investigation on the matrix set (2) or (2′) towhich the foregoing precoding matrix W belongs that, the foregoingprecoding matrix W may match actually deployed antenna configuration.Because a granularity of a value of θ is

$\frac{\pi}{16},$

more precise spatial quantization is achieved, and feedback precision ofCSI can be improved. In addition, two columns of the precoding matrix Ware orthogonal to each other, which can reduce inter-layer interference.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the following matrix set:

$\begin{matrix}{\begin{Bmatrix}{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\; \theta} & ^{j\theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\^{{j\; \theta}\;} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\{- ^{j\; \theta}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},} \\{{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\^{j\; \theta} & ^{j\theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\^{{j\; \theta}\;} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\{- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\1 & {- 1} & {- 1} \\{- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}}\end{bmatrix}}}\end{Bmatrix}{{{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,}} & (3)\end{matrix}$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

Similarly, it can be learned from investigation on the matrix set (3) towhich the foregoing precoding matrix W belongs that, the foregoingprecoding matrix W may match actually deployed antenna configuration.Because a granularity of a value of θ is

$\frac{\pi}{16},$

more precise spatial quantization is achieved, and feedback precision ofCSI can be improved. In addition, two columns of the precoding matrix Ware orthogonal to each other, which can reduce inter-layer interference.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the following matrix set:

$\begin{matrix}{\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\theta} & {- ^{j\; \theta}} \\1 & 1 & {- 1} & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & {- ^{j\; \theta}} & ^{j\; \theta} & {- ^{j\; \theta}} \\j & j & {- j} & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}} & (4) \\{\left\{ {{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\theta}} & {- ^{j\; \theta}} \\1 & {- 1} & 1 & {- 1} \\^{j\; \theta} & {- ^{{j\; \theta}\;}} & {- ^{j\; \theta}} & ^{j\; \theta}\end{bmatrix}},{\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\^{j\; \theta} & ^{j\; \theta} & {- ^{j\; \theta}} & {- ^{j\; \theta}} \\j & {- j} & j & {- j} \\{j\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {{- j}\; ^{j\; \theta}} & {j\; ^{j\; \theta}}\end{bmatrix}}} \right\} {{{{where}\mspace{14mu} \theta} = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,{and}}} & (5)\end{matrix}$

└i₂/2┘ indicates that its value is the greatest integer not greater thani₂/2.

Similarly, it can be learned from investigation on the matrix set (4) or(5) to which the foregoing precoding matrix W belongs that, theforegoing precoding matrix W may match actually deployed antennaconfiguration. Because a granularity of a value of θ is

$\frac{\pi}{4},$

more precise spatial quantization is achieved, and feedback precision ofCSI can be improved. In addition, two columns of the precoding matrix Ware orthogonal to each other, which can reduce inter-layer interference.

Step S103: Send a precoding matrix indicator PMI to the base station,where the PMI is corresponding to the selected precoding matrix W.

In this embodiment of the present invention, the precoding matrixindicator PMI may include only one specific value, and the PMI directlyindicates the selected precoding matrix. For example, altogether 256different precoding matrices may be selected from the matrix set (1) or(2), and then PMI=0, . . . , 255 may be used to respectively indicatethe precoding matrices whose index values are 0, 1, . . . , 255.Therefore, as an embodiment of the present invention in which aprecoding matrix indicator PMI is sent to the base station and the PMIis corresponding to the selected precoding matrix, the precoding matrixindicator PMI may be an index value corresponding to a precoding matrixW in a codebook. Because a base station side also has the codebook, thebase station may obtain, according to the PMI, a precoding matrixselected by a UE from the codebook.

According to another aspect, because the index values i₁ and i₂ canuniquely determine a precoding matrix W, as another embodiment of thepresent invention in which a precoding matrix indicator PMI is sent tothe base station and the PMI is corresponding to the selected precodingmatrix, a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ may be sent to the base station, and arerespectively corresponding to the index values i₁ and i₂ that areassociated with the selected precoding matrix. Because a base stationside also has the codebook, the base station may obtain, according tothe first precoding matrix indicator PMI₁ and the second precodingmatrix indicator PMI₂, a precoding matrix selected by a UE from thecodebook. For ease of the following description, a precoding matrixindicator PMI₁ and a precoding matrix indicator PMI₂ are respectivelyused to indicate corresponding precoding matrix indicators indicated byi₁ and i₂. In this embodiment of the present invention, the PMI₁ and thePMI₂ have different time domain or frequency domain granularities, orare obtained based on different subframe periods or sub-band sizes. Forexample, the precoding matrix indicator PMI₁ and the precoding matrixindicator PMI₂ respectively indicate channel characteristics withdifferent periods or bandwidth, or are obtained based on differentsubframe periods or sub-band sizes. Further, the precoding matrixindicator PMI₁ and the precoding matrix indicator PMI₂ are sent to thebase station in different time periods.

When a precoding matrix indicator PMI is sent to a base station, theprecoding matrix indicator PMI may be sent to the base station by a userequipment through a physical uplink control channel (PUCCH) or aphysical uplink shared channel (PUSCH). It should be noted that, theprecoding matrix W in this embodiment of the present invention may be aprecoding matrix obtained after row or column displacement. For example,different antenna numbers correspondingly lead to row displacement ofthe precoding matrix.

It can be learned from the foregoing method for feeding back channelstate information according to this embodiment of the present inventionthat, a user equipment may select a precoding matrix from a codebookbased on a received reference signal, and send a precoding matrixindicator corresponding to the selected precoding matrix to the basestation. The codebook includes at least one precoding matrix W, and acolumn vector of the precoding matrix W may be expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector. The foregoingcodebook structure may match actually deployed antenna configuration,for example, configuration of a four-port dual-polarized antenna or auniform linear array antenna; phases θ and φ are flexibly selected,which cannot only further improve quantization precision as required,but also achieve balance between overheads and the quantizationprecision. In addition, column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which improves system throughput.

With reference to FIG. 1, the foregoing embodiment describes in detail amethod for feeding back channel state information according to theembodiment of the present invention from a perspective of a UE; withreference to FIG. 2, the following describes a method for feeding backchannel state information according to an embodiment of the presentinvention from a perspective of a base station.

FIG. 2 is a method for feeding back channel state information accordingto another embodiment of the present invention. The method in FIG. 2 isimplemented by a base station, which, for example, may be a node B(NodeB), an access point (AP), a transmission point (TP), an evolvednode B (eNB), or a relay (Relay).

It should be understood that description about a UE side in interactionbetween a UE and a base station, and related characteristics andfunctions of the UE and the base station is corresponding to descriptionabout a base station side. For brevity, details are not described hereinagain.

The following describes a method illustrated in FIG. 2, which mainlyincludes step S201 and step S202. Detailed description is as follows:

Step S201: Send a reference signal to a user equipment UE.

Specifically, the reference signal may include a CSI RS, a DM RS, a CRS,or the like. The base station may instruct the UE to receive thereference signal through higher layer signaling such as RRC signaling ordownlink control information DCI; or the base station sends thereference signal over a resource or a subframe of a correspondingreference signal based on a cell identity ID. This embodiment of thepresent invention sets no limitation on a specific manner of sending areference signal.

Step S202: Receive a precoding matrix indicator PMI sent by the UE,where the PMI is corresponding to a precoding matrix W that is selectedby the UE from a codebook based on the reference signal, and a columnvector of the precoding matrix W may be expressed as α[v e^(jφ)v]^(T),v=[1 e^(jθ)], where α is a constant, θ and φ are phases, and [ ]^(T)indicates transposing of a matrix or vector.

Specifically, values of phases θ and φ may be flexibly selectedaccording to a requirement of quantization precision.

Further, column vectors of the precoding matrix W may be orthogonal toeach other, that is, W meets W^(H)W=α²I, where W^(H) indicates aconjugate transpose of the matrix W, and I is an identity matrix. Theforegoing structure divides antenna ports into two groups; a vector vmay match channel characteristics corresponding to each antenna group ofthe two groups, and a phase between the two antenna port groups may beexpressed by φ.

As an embodiment of the present invention, the precoding matrix W is atleast one matrix in the matrix set shown in the expression (1), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (2) or(2′), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (3),where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (4) or(5), where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/2.

It can be learned from investigation on the foregoing precoding matrix Wthat, the foregoing matrix structure may match actually deployed antennaconfiguration, for example, configuration of a four-port dual-polarizedantenna or a uniform linear array antenna. Phases θ and φ are flexiblyselected, which cannot only further improve quantization precision asrequired, but also achieve balance between overheads and thequantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

The codebook is known to both the base station and the UE. As anotherembodiment of the present invention, the precoding matrix indicator PMImay include only one specific value, and the PMI directly indicates theselected precoding matrix. For example, altogether 256 differentprecoding matrices may be selected from the matrix set (1) or (2), andthen PMI=0, . . . , 255 may be used to respectively indicate theprecoding matrices whose index values are 0, 1, . . . , 255. In thiscase, the base station may obtain, according to the PMI, the precodingmatrix selected by the UE from the codebook.

As another embodiment of the present invention, the precoding matrixindicator PMI may include two indexes, that is, a first precoding matrixindicator PMI₁ and a second precoding matrix indicator PMI₂, where thePMI₁ and the PMI₂ are respectively corresponding to index values i₁ andi₂ that are associated with the selected precoding matrix. The basestation may obtain, according to the PMI₁ and the PMI₂, the precodingmatrix selected by the UE from the codebook.

When a precoding matrix indicator PMI sent by a user equipment UE isreceived, the PMI may be received by a base station through a PUCCH or aPUSCH. It should be noted that, the precoding matrix W in thisembodiment of the present invention may be a precoding matrix obtainedafter row or column displacement. For example, different antenna numberscorrespondingly lead to row displacement of the precoding matrix.

It can be learned from the foregoing method for feeding back channelstate information according to this embodiment of the present inventionthat, abase station sends a reference signal and receives a precodingmatrix indicator PMI sent by a UE, where the PMI is corresponding to aprecoding matrix that is selected by the UE from a codebook based on thereference signal. The codebook includes at least one precoding matrix W,and a column vector of the precoding matrix W may be expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases, []^(T) and indicates transposing of a matrix or vector. The foregoingcodebook structure may match actually deployed antenna configuration,for example, configuration of a four-port dual-polarized antenna or auniform linear array antenna; phases θ and φ are flexibly selected,which cannot only further improve quantization precision as required,but also achieve balance between overheads and the quantizationprecision. In addition, column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which improves system throughput.

The following describes in detail a system for feeding back channelstate information, a user equipment, and a base station according to thepresent invention. Referring to FIG. 3, FIG. 3 is a schematic diagram ofstructural composition of a system for feeding back channel stateinformation according to an embodiment of the present invention. Thesystem according to this embodiment of the present invention includes auser equipment 30 and a base station 40. A structure of the userequipment 30 is shown in FIG. 4, and a structure of the base station 40is shown in FIG. 5.

Referring to FIG. 4, FIG. 4 is a schematic structural diagram of theuser equipment 30 according to the embodiment of the present invention,and the user equipment 30 includes a receiving module 301, a selectingmodule 302, and a sending module 303, where the receiving module 301 maybe implemented by a receiver in the user equipment 30 or a softwaremodule/unit or a hardware module/unit of the receiver of the userequipment 30, the selecting module 302 may be implemented by a processorin the user equipment 30 or a software module/unit or a hardwaremodule/unit of the processor of the user equipment 30, and the sendingmodule 303 may be implemented by a transmitter in the user equipment 30or a software module/unit or a hardware module/unit of the transmitterof the user equipment 30.

The receiving module 301 is configured to receive a reference signalsent by a base station. The reference signal sent by the base stationmay include a channel state information reference signal (CSI RS), ademodulation reference signal (DM RS), a cell-specific reference signal(CRS), or the like. The user equipment may obtain the reference signalby receiving an eNB notification, for example, by receiving radioresource control (RRC) signaling or downlink control information (DCI);or the user equipment obtains resource configuration of the referencesignal based on a cell identity ID and then obtains the reference signalfrom a corresponding resource or subframe. This embodiment of thepresent invention sets no limitation on a specific manner of receiving areference signal.

It should be understood that the foregoing reference signal iscorresponding to an antenna port; the reference signal may becorresponding to a physical antenna or an antenna array element, ormaybe corresponding to a virtual antenna, where the virtual antenna is aweighted combination of a physical antenna and an antenna array element.

The selecting module 302 is configured to select a precoding matrix Wfrom a codebook based on the reference signal received by the receivingmodule 301, where a column vector of the precoding matrix W may beexpressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θand φ are phases, and indicates transposing of a matrix or vector.

Specifically, values of phases θ and φ may be flexibly selectedaccording to a requirement of quantization precision.

Further, column vectors of the precoding matrix W may be orthogonal toeach other, that is, W meets W^(H)W=α²I, where W^(H) indicates aconjugate transpose of the matrix W, and I is an identity matrix. Theforegoing structure divides antenna ports into two groups; a vector vmay match channel characteristics corresponding to each antenna group ofthe two groups, and a phase between the two antenna port groups may beexpressed by φ. The foregoing structure may match actually deployedantenna configuration, for example, configuration of a four-portdual-polarized antenna or a uniform linear array antenna. Phases θ and φare flexibly selected, which cannot only further improve quantizationprecision as required, but also achieve balance between overheads andthe quantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

It can be learned from the foregoing embodiment of the present inventionthat, a user equipment may select a precoding matrix from a codebookbased on a received reference signal, and send a precoding matrixindicator corresponding to the selected precoding matrix W to a basestation, where the codebook includes at least one precoding matrix W,and a column vector of the precoding matrix W may be expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector. The foregoingcodebook structure may match actually deployed antenna configuration,for example, configuration of a four-port dual-polarized antenna or auniform linear array antenna; phases θ and φ are flexibly selected,which cannot only further improve quantization precision as required,but also achieve balance between overheads and the quantizationprecision. In addition, column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which can improve precodingprecision, thereby improving a data transmission rate and systemthroughput.

The selecting module 302 shown in FIG. 4 maybe specifically configuredto acquire a channel estimation value based on the reference signal, andselect a precoding matrix from a codebook according to the channelestimation value.

It should be noted that, this embodiment of the present invention setsno limitation on a specific manner of selecting a precoding matrix.Optionally, a precoding matrix is selected from the codebook accordingto a predefined criterion, such as a criterion of channel capacity orthroughput maximization, or a criterion of chordal distanceminimization. Selecting a precoding matrix based on a predefinedcriterion is an existing technology, and details are not describedherein again.

As an embodiment of the present invention, the precoding matrix W is atleast one matrix in the matrix set shown in the expression (1), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (2) or(2′), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan └i₂/4┘.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (3),where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

indicates └i₂/4┘ indicates that its value is the greatest integer notgreater than i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (4) or(5), where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/2┘ indicates that its value is the greatest integer not greaterthan i₂/2.

It can be learned from investigation on the foregoing precoding matrix Wthat, the foregoing matrix structure may match actually deployed antennaconfiguration, for example, configuration of a four-port dual-polarizedantenna or a uniform linear array antenna. Phases θ and φ are flexiblyselected, which cannot only further improve quantization precision asrequired, but also achieve balance between overheads and thequantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

The sending module 303 is configured to send a precoding matrixindicator PMI to the base station, where the PMI is corresponding to theprecoding matrix W selected by the selecting module 302. The userequipment may send the precoding matrix indicator PMI to the basestation through a PUCCH or a PUSCH.

As an embodiment of the present invention, the precoding matrixindicator PMI may include only one specific value, and the PMI directlyindicates the selected precoding matrix. For example, altogether 256different precoding matrices maybe selected from the matrix set (1) or(2), and then PMI=0, . . . , 255 may be used to respectively indicatethe precoding matrices whose index values are 0, 1, . . . , 255.Therefore, as an embodiment of the present invention in which aprecoding matrix indicator PMI is sent to the base station and the PMIis corresponding to the selected precoding matrix, the precoding matrixindicator PMI may be an index value corresponding to a precoding matrixW in a codebook. Because a base station side also has the codebook, thebase station may obtain, according to the PMI, the precoding matrixselected by the UE from the codebook.

As another embodiment of the present invention, the precoding matrixindicator PMI may include two indexes, that is, a first precoding matrixindicator PMI₁ and a second precoding matrix indicator PMI₂, where thePMI₁ and the PMI₂ are respectively corresponding to index values i₁ andi₂ that are associated with the selected precoding matrix. The basestation may obtain, according to the first precoding matrix indicatorPMI₁ and the second precoding matrix indicator PMI₂, the precodingmatrix selected by the UE from the codebook.

In this embodiment of the present invention, the PMI₁ and the PMI₂ havedifferent time domain or frequency domain granularities, or are obtainedbased on different subframe periods or sub-band sizes. For example, theprecoding matrix indicator PMI₁ and the precoding matrix indicator PMI₂respectively indicate channel characteristics with different periods orbandwidth, or are obtained based on different subframe periods orsub-band sizes. Further, the precoding matrix indicator PMI₁ and theprecoding matrix indicator PMI₂ are sent to the base station indifferent time periods.

When a precoding matrix indicator PMI is sent to a base station, theprecoding matrix indicator PMI may be sent to the base station by a userequipment through a PUCCH or a PUSCH. It should be noted that, theprecoding matrix Win this embodiment of the present invention may be aprecoding matrix obtained after row or column displacement. For example,different antenna numbers correspondingly lead to row displacement ofthe precoding matrix.

It can be learned from the foregoing user equipment according to thisembodiment of the present invention that, the user equipment may selecta precoding matrix from a codebook based on a received reference signal,and send a precoding matrix indicator corresponding to the selectedprecoding matrix to a base station. The codebook includes at least oneprecoding matrix W, and a column vector of the precoding matrix W may beexpressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θand φ are phases, and [ ]^(T) indicates transposing of a matrix orvector.

The foregoing codebook structure may match actually deployed antennaconfiguration, for example, configuration of a four-port dual-polarizedantenna or a uniform linear array antenna; phases θ and φ are flexiblyselected, which cannot only further improve quantization precision asrequired, but also achieve balance between overheads and thequantization precision. In addition, column vectors of the precodingmatrix W are orthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which improves system throughput.

It should be noted that, in the foregoing implementation manner of theuser equipment, division of functional modules is merely used as anexample, and the foregoing functions may be allocated to differentfunctional modules according to an actual requirement, for example,according to a corresponding hardware configuration requirement or forease of software implementation; that is, an internal structure of theuser equipment is divided into different functional modules, to completeall or some of the functions described above. In addition, in an actualapplication, corresponding functional modules in this embodiment may beimplemented by corresponding hardware, or may be implemented bycorresponding hardware by implementing corresponding software. Forexample, the foregoing receiving module may be hardware that has afunction of implementing the foregoing receiving a reference signal sentby a base station, such as a receiver, or may be a universal processoror another hardware device that can execute a corresponding computerprogram to complete the foregoing functions. For another example, theforegoing selecting module may be hardware that has a function ofexecuting the foregoing selecting a precoding matrix W from a codebookbased on a reference signal received by the receiving module (orreceiver), such as a precoding matrix determiner, or may be a universalprocessor or another hardware device that can execute a correspondingcomputer program to complete the foregoing functions. (The principle ofthe foregoing description may be applicable to each embodiment providedin this specification.)

Referring to FIG. 5, FIG. 5 is a schematic structural diagram of a basestation according to an embodiment of the present invention. The basestation includes a second sending module 401 and a second receivingmodule 402, where the second sending module 401 may be implemented by atransmitter in a base station 40 or a software module/unit or a hardwaremodule/unit of the transmitter in the base station 40; the secondreceiving module 402 may be implemented by a receiver in the basestation 40 or a software module/unit or a hardware module/unit of thereceiver in the base station 40; or the second sending module 401 andthe second receiving module 402 may be implemented by a processor in thebase station 40 or a software module/unit or a hardware module/unit ofthe processor in the base station 40.

The second sending module 401 is configured to send a reference signalto a user equipment UE.

Specifically, the reference signal may include a CSI RS, a DM RS, a CRS,or the like. The base station may instruct the UE to receive thereference signal through higher layer signaling such as RRC signaling ordownlink control information DCI; or the base station sends thereference signal over a resource or a subframe of a correspondingreference signal based on a cell identity ID. This embodiment of thepresent invention sets no limitation on a specific manner of sending areference signal.

It should be understood that the foregoing reference signal iscorresponding to an antenna port; the reference signal may becorresponding to a physical antenna or an antenna array element, ormaybe corresponding to a virtual antenna, where the virtual antenna is aweighted combination of a physical antenna and an antenna array element.

The second receiving module 402 is configured to receive a precodingmatrix indicator PMI sent by the user equipment UE, where the PMI iscorresponding to a precoding matrix W that is selected by the UE from acodebook based on the reference signal, and a column vector of theprecoding matrix W may be expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)],where α is a constant, θ and φ are phases, and indicates transposing ofa matrix or vector.

Specifically, values of phases θ and φ may be flexibly selectedaccording to a requirement of quantization precision.

Further, column vectors of the precoding matrix W may be orthogonal toeach other, that is, W meets W^(H)W=α²I, where W^(H) indicates aconjugate transpose of the matrix W, and I is an identity matrix. Theforegoing structure divides antenna ports into two groups; a vector vmay match channel characteristics corresponding to each antenna group ofthe two groups, and a phase between the two antenna port groups may beexpressed by φ. The foregoing structure may match actually deployedantenna configuration, for example, configuration of a four-portdual-polarized antenna or a uniform linear array antenna. Phases θ and φare flexibly selected, which cannot only further improve quantizationprecision as required, but also achieve balance between overheads andthe quantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

As an embodiment of the present invention, the precoding matrix W is atleast one matrix in the matrix set shown in the expression (1), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (2) or(2′), where

${\theta = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$

and └i₂/4┘ indicates that its value is the greatest integer not greaterthan i₂/4.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (3),where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/4} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},15,$

and └i²/4┘ indicates that its value is the greatest integer not greaterthan └i₂4┘.

As another embodiment of the present invention, the precoding matrix Wis at least one matrix in the matrix set shown in the expression (4) or(5), where

${\theta = {\frac{\pi}{8}\left( {{4i_{1}} + {2\left\lfloor {i_{2}/2} \right\rfloor}} \right)}},{i_{1} = 0},1,2,3,{i_{2} = 0},\ldots \mspace{14mu},7,$

and └i₂/2┘ indicates that its value is the greatest integer not greaterthan i₂/2.

It can be learned from investigation on the foregoing precoding matrix Wthat, the foregoing matrix structure may match actually deployed antennaconfiguration, for example, configuration of a four-port dual-polarizedantenna or a uniform linear array antenna. Phases θ and φ are flexiblyselected, which cannot only further improve quantization precision asrequired, but also achieve balance between overheads and thequantization precision. Column vectors of the precoding matrix W areorthogonal to each other, which further reduces inter-layerinterference, thereby improving a transmission rate and spectralefficiency of a system.

The codebook is known to both the base station and the UE. As anotherembodiment of the present invention, the precoding matrix indicator PMImay include only one specific value, and the PMI directly indicates theselected precoding matrix. For example, altogether 256 differentprecoding matrices may be selected from the matrix set (1) or (2), andthen PMI=0, . . . , 255 may be used to respectively indicate theprecoding matrices whose index values are 0, 1, . . . , 255. In thiscase, the base station may obtain, according to the PMI, the precodingmatrix selected by the UE from the codebook.

As another embodiment of the present invention, the precoding matrixindicator PMI may include two indexes, that is, a first precoding matrixindicator PMI₁ and a second precoding matrix indicator PMI₂, where thePMI₁ and the PMI₂ are respectively corresponding to index values i₁ andi₂ that are associated with the selected precoding matrix. The basestation may obtain, according to the PMI₁ and the PMI₂, the precodingmatrix selected by the UE from the codebook.

When a precoding matrix indicator PMI sent by a user equipment UE isreceived, the PMI may be received by a base station through a PUCCH or aPUSCH. It should be noted that, the precoding matrix W in thisembodiment of the present invention may be a precoding matrix obtainedafter row or column displacement. For example, different antenna numberscorrespondingly lead to row displacement of the precoding matrix.

It can be learned from the foregoing base station for feeding backchannel state information according to this embodiment of the presentinvention that, the base station sends a reference signal and receives aprecoding matrix indicator PMI sent by a UE, where the PMI iscorresponding to a precoding matrix that is selected by the UE from acodebook based on the reference signal. The codebook includes at leastone precoding matrix W, and a column vector of the precoding matrix Wmay be expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], where α is aconstant, θ and φ are phases, and indicates transposing of a matrix orvector. The foregoing codebook structure may match actually deployedantenna configuration, for example, configuration of a four-portdual-polarized antenna or a uniform linear array antenna; phases θ and φare flexibly selected, which cannot only further improve quantizationprecision as required, but also achieve balance between overheads andthe quantization precision. In addition, column vectors of the precodingmatrix W are orthogonal to each other, which further reduces inter-layerinterference. After the user equipment feeds back the precoding matrixindicator corresponding to the precoding matrix W to the base station,the base station performs precoding on a sent signal according to thefed back precoding matrix indicator, which improves system throughput.

An embodiment of the present invention further provides a computerstorage medium, where the computer storage medium may store a program,and when the program is executed, the steps illustrated in FIG. 1 orFIG. 2 are performed.

It should be noted that content such as information exchange between themodules/units of the foregoing apparatus and the execution processesthereof is based on the same idea as the method embodiments of thepresent invention, and produces the same technical effects as the methodembodiments of the present invention. For the specific content, refer tothe description in the method embodiments of the present invention, andthe details are not described herein again.

A person of ordinary skill in the art may understand that all or some ofthe steps of the foregoing embodiments may be implemented by a programthat instructs related hardware, for example, one or more or all of thefollowing methods:

Method 1: receiving a reference signal sent by a base station; selectinga precoding matrix W from a codebook according to the reference signal,where a column vector of the precoding matrix W is expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], where α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector; and sending aprecoding matrix indicator PMI corresponding to the selected precodingmatrix to the base station.

Method 2: sending a reference signal to a user equipment UE; receiving aprecoding matrix indicator PMI sent by the UE, where the PMI iscorresponding to a precoding matrix W that is selected by the UE from acodebook based on the reference signal, and a column vector of theprecoding matrix W is expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], whereα is a constant, θ and φ are phases, and indicates transposing of amatrix or vector.

A person of ordinary skill in the art may understand that all or a partof the steps of the methods in the embodiments may be implemented by aprogram instructing related hardware. The program may be stored in acomputer readable storage medium. The storage medium may include: aread-only memory (ROM), a random access memory (RAM), a magnetic disk,or an optical disc.

The foregoing has described a method for feeding back channel stateinformation, a user equipment, and a base station according to theembodiments of the present invention in detail. Specific examples areused in this specification to expound the principles and implementationmanners of the present invention. The description of the embodiments ismerely intended to help understand the method of the present inventionand core ideas thereof. In addition, persons of ordinary skill in theart can make various modifications and variations to the invention withrespect to specific implementation manners and application scopesaccording to the ideas of the invention. In conclusion, the content ofthe specification shall not be construed as a limitation on the presentinvention.

What is claimed is:
 1. A method for feeding back channel stateinformation, the method comprising: receiving a reference signal sent bya base station; selecting a precoding matrix W from a codebook based onthe reference signal, wherein a column vector of the precoding matrix Wis expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)], wherein α is a constant,θ and φ are phases, and indicates transposing of a matrix or vector; andsending a precoding matrix indicator (PMI) to the base station, whereinthe PMI corresponds to the selected precoding matrix W.
 2. The methodaccording to claim 1, wherein the precoding matrix W is at least onematrix in the following matrix set:$\left\{ {{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\1 \\^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\j \\{j}^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- 1} \\{- ^{j\theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- j} \\{- {j}^{j\theta}}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},$└i₂4┘ indicates indicates the greatest integer not greater than i₂/4,i₁=0, . . . , 15, and i₂=0, . . . ,
 15. 3. The method according to claim1, wherein the precoding matrix W is at least one matrix in thefollowing matrix set: $\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\1 & {- 1} \\^{j\theta} & {- ^{j\theta}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}$$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\1 & {- 1} \\^{j\theta} & {- ^{j{({\theta + \phi})}}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\j & {- j} \\{j}^{j\theta} & {{- {j}^{j{({\theta + \phi})}}}\;}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 4. Themethod according to claim 2, wherein sending a precoding matrixindicator (PMI) to the base station comprises: sending a first precodingmatrix indicator PMI₁ and a second precoding matrix indicator PMI₂ tothe base station, wherein the first precoding matrix indicator PMI₁ andthe second precoding matrix indicator PMI₂ are respectively used toindicate indexes i₁ and i₂ corresponding to the selected precodingmatrix W.
 5. A method for feeding back channel state information, themethod comprising: sending a reference signal to a user equipment (UE);receiving a precoding matrix indicator (PMI) sent by the UE, wherein thePMI is corresponding to a precoding matrix W that is selected by the UEfrom a codebook based on the reference signal, and a column vector ofthe precoding matrix W is expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)],wherein α is a constant, θ and θ are phases, and [ ]^(T) indicatestransposing of a matrix or vector.
 6. The method according to claim 5,wherein the precoding matrix W is at least one matrix in the followingmatrix set: $\left\{ {{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\1 \\^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\j \\{j}^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- 1} \\{- ^{j\theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- j} \\{- {j}^{j\theta}}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},$└i₂/4┘ indicates the greatest integer not greater than i₂/4, i₁=0, . . ., 15, and i₂=0, . . . ,
 15. 7. The method according to claim 5, whereinthe precoding matrix W is at least one matrix in the following matrixset: $\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\1 & {- 1} \\^{j\theta} & {- ^{j\theta}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}}\end{bmatrix}}} \right\}$ or$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\1 & {- 1} \\^{j\theta} & {- ^{j{({\theta + \phi})}}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\j & {- j} \\{j}^{j\theta} & {{- {j}^{j{({\theta + \phi})}}}\;}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 8. Themethod according to claim 6, wherein receiving a precoding matrixindicator (PMI) sent by the UE comprises: receiving a first precodingmatrix indicator PMI₁ and a second precoding matrix indicator PMI₂ thatare sent by the UE, wherein the first precoding matrix indicator PMI₁and the second precoding matrix indicator PMI₂ are respectively used toindicate indexes i₁ and i₂ corresponding to the selected precodingmatrix.
 9. A user equipment, comprising: a receiving module, configuredto receive a reference signal sent by a base station; a selectingmodule, configured to select a precoding matrix W from a codebook basedon the reference signal received by the receiving module, wherein acolumn vector of the precoding matrix W is expressed as α[ve^(jφ)v]^(T), v=[1 e^(jθ)], wherein α is a constant, θ and φ are phases,and [ ]^(T) indicates transposing of a matrix or vector; and a sendingmodule, configured to send a precoding matrix indicator (PMI) to thebase station, wherein the PMI is corresponding to the precoding matrix Wselected by the selecting module.
 10. The user equipment according toclaim 9, wherein the precoding matrix W is at least one matrix in thefollowing matrix set: $\left\{ {{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\1 \\^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\j \\{j}^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- 1} \\{- ^{j\theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- j} \\{- {j}^{j\theta}}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 11. Theuser equipment according to claim 9, wherein the precoding matrix W isat least one matrix in the following matrix set:$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\1 & {- 1} \\^{j\theta} & {- ^{j\theta}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}$$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\1 & {- 1} \\^{j\theta} & {- ^{j{({\theta + \phi})}}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\j & {- j} \\{j}^{j\theta} & {{- {j}^{j{({\theta + \phi})}}}\;}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 12. Theuser equipment according to claim 10, wherein the sending module isconfigured to: send a first precoding matrix indicator PMI₁ and a secondprecoding matrix indicator PMI₂ to the base station, wherein the firstprecoding matrix indicator PMI₁ and the second precoding matrixindicator PMI₂ are respectively used to indicate indexes i₁ and i₂corresponding to the selected precoding matrix.
 13. A base station,comprising: a second sending module, configured to send a referencesignal to a user equipment (UE); a second receiving module, configuredto receive a precoding matrix indicator (PMI) sent by the UE, whereinthe PMI is corresponding to a precoding matrix W that is selected by theUE from a codebook based on the reference signal, and a column vector ofthe precoding matrix W is expressed as α[v e^(jφ)v]^(T), v=[1 e^(jθ)],wherein α is a constant, θ and φ are phases, and [ ]^(T) indicatestransposing of a matrix or vector.
 14. The base station according toclaim 13, wherein the precoding matrix W is at least one matrix in thefollowing matrix set: $\left\{ {{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\1 \\^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\j \\{j}^{j\theta}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- 1} \\{- ^{j\theta}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\^{j\theta} \\{- j} \\{- {j}^{j\theta}}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 15. Thebase station according to claim 13, wherein the precoding matrix W is atleast one matrix in the following matrix set:$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\1 & {- 1} \\^{j\theta} & {- ^{j\theta}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j\theta} \\j & {- j} \\{j}^{j\theta} & {- {j}^{j\theta}}\end{bmatrix}}} \right\} \mspace{14mu} {or}$$\left\{ {{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\1 & {- 1} \\^{j\theta} & {- ^{j{({\theta + \phi})}}}\end{bmatrix}},{\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\^{j\theta} & ^{j{({\theta + \phi})}} \\j & {- j} \\{j}^{j\theta} & {{- {j}^{j{({\theta + \phi})}}}\;}\end{bmatrix}}} \right\}$${{{wherein}\mspace{14mu} \theta} = {\frac{\pi}{16}\left( {{2i_{1}} + \left\lfloor {i_{2}/4} \right\rfloor} \right)}},{i_{1} = 0},\ldots \mspace{14mu},15,{i_{2} = 0},\ldots \mspace{14mu},15,{\phi = \frac{\pi}{16}},\frac{\pi}{8},\ldots \mspace{14mu},$and └i₂/4┘ indicates the greatest integer not greater than i₂/4.
 16. Thebase station according to claim 14, wherein the second receiving moduleis configured to: receive a first precoding matrix indicator PMI₁ and asecond precoding matrix indicator PMI₂ that are sent by the userequipment to the base station, wherein the first precoding matrixindicator PMI₁ and the second precoding matrix indicator PMI₂ arerespectively used to indicate indexes i₁ and i₂ corresponding to theselected precoding matrix.